Zinc sulfide and zinc cadmium sulfide phosphors are well known and have been used commercially for many years. Such phosphors activated with silver or copper are commonly used as the green phosphor in color television cathode ray tubes. Zinc cadmium sulfide phosphors activated with manganese also are known.
Alkaline earth sulfide phosphors, activated with a variety of elements, have been reported ("Some Aspects of the Luminescence of Solids", by Kroger, Elsevier Publishing Co., Inc., 1948), but have not found substantial commercial use. Barium zinc sulfide has been previously reported as a chemical compound by Schnering and Hoppe in Z. Anorg u. Allgem Chem., 312, p. 99 (1961), and Malur, Z. fur Chemie, 5, p. 399 (1965). However, the compound reported by these investigators is different from the novel compound to which this invention relates. The earlier investigators reported on a Ba.sub.2 ZnS.sub.3 species which crystallized in the beta form crystal structure. The compounds claimed in this patent application are different materials in that they crystallize in the alpha form structure and exhibit different luminescent properties. The discovery of this new crystal form for Ba.sub.2 ZnS.sub.3 is completely unexpected from what has been reported in the literature.
The most satisfactory red-emitting phosphors for cathode ray tube use are the rare earth phosphors, especially the rare earth oxides and oxysulfides such as yttrium oxysulfide or yttrium oxide, both activated with europium, and gadolinium oxide activated with europium Yttrium vanadate activated with europium has also been used successfully. The rare earth phosphors are all relatively expensive and no relatively inexpensive red-emitting phosphors have thus far been developed which can equal them in cathode ray tube use.